Method of making hydrous sodium silicates



Patented Nov. 26, 194:0v

. UNITED STATES METHOD OF MAKING HYDROUS SODIUM SILICATES George R.McDaniel, Cincinnati, Ohio, assignor to Diamond Alkali Company,Pittsburgh, Pa., a corporation of Delaware N Drawing.

Application August 26, 1938,

Serial No. 226,988

7 Claims.

which are more alkaline than the sodium metaand sesquisilicates. Thesemore alkaline silicate compositions, to which both the present inventionand the invention of my copending application are directed, arecomprised of from approximately 1.75 to 2.25 molecular parts of sodiumoxide to each molecular part of silicon dioxide, together with aquantity of water which is present as water of hydration. Thecompositions of this range are known broadly in the industry asorthosilicates, though, from the strict chemical point of view, theorthosilicate is a chemical composition in which two molecular parts ofsodium 25 oxide are combined with one molecular part of silica. Just asin thecase of a metasilicate, one part of the metal oxide is combinedwith one part of silica; and in the sesquior pyrosilicate, one andone-half parts of the oxide is present for each molecular part ofsilicon dioxide.

In the copending applicationthere isdisclosed a process for making theseorthosilicate materials in the form of stable and yet hydrated crystals,particles and flakes. This process is predicated upon the discovery thatliquid solutions which are composed of silicon dioxide and sodium oxidein the molecular proportions appropriate for providing a desired ratioof components in the ortho range may be crystallized 40 by theapplication of heat. These solutions contain an amount of water which issufiicient to provide the desired hydrate, but which is not in suchexcess that evaporation of water is requisite before crystallization canbe made to take place. While it has always been the experience thatcrystallisis is induced by supercooling, the process which is disclosedin the copending application is based, paradoxically, upon the discoverythat the ortho liquids there disclosed readily are crystallizable by theapplication of heat, rather than the removal of it. The process,therefore, may be and is designated a process of thermalcrystallization. T

In the process of thermal crystallization which is disclosedin thecopending application the ortho liquors are established by dissolutionof a suitable material providing silicon dioxide, and a suitablematerial providing sodium oxide, together with or in the presence of aquantity of water which is limited in amount, but which is ,5 sufiicientto enable the formation of a crystalline hydrate. For instance, dry 76%lye flake is dissolved in molten metasilicate liquor in such quantitythat the proportion of sodium oxide to silicon dioxide is within therange of approximately 10 1.75 to 2.25 Na2O to 15102. The water content,which is obtained either from the silicate liquor, or by directaddition, is such that the liquid or liquor which is so established willbe sufiicient to provide approximately 5 to 7 molecules 0115 water ofhydration without there being any later substantial evaporation ofwater. Next, this liquid is heated, for the thermal crystallization ofit, to elevated temperature, for instance, to a temperature within therange of approximately "20 100-150" C. With this application of heat,transformation of the liquid into a crystallitic solid takes placepromptly and is complete after a short period'of time. In the generalprocess, therefore, a crystallitic solid of a given com- 25 positionwithin the range specified is prepared by heating to an elevatedtemperature a liquid of the same composition.

The improvement of the invention disclosed in the copending application,to which the present patent application is directed, is predicated uponthe concept of preparing the liquid which is to be transformed into thecrystallitic solid at a temperature which is sufliciently high to efiectsolidification and crystallization of the liquor when it is permitted tostand for a short period without subsequent or further additions ofheat.

In the present process the material providing sodium oxide, the materialproviding silicon dioxide and the water which is contained in the sourceof silicon dioxide, or which is added by direct addition, are broughttogether to constitute the ortho liquor of the desired chemicalproportions,

at a temperature which is sufliciently high to enable this liquor tocrystallize of its own voli tion when it is permitted to stand for ashort period.

The crystallization takes place without loss of water, exceptinginconsequential amounts that do not disturb or prevent the desiredhydrates from being obtained. In the present method, therefore, ortholiquor containing an amount of sodium oxide which is sufficient toprovide approximately 1.75 to 2.25 molecular parts for each molecularpart of silicon dioxide, and containing an amount of water which issufficient to provide approximately 5 to 7 molecules of water ofhydration without substantial evaporation is prepared at a temperaturesufficiently high to enable this liquor to crystallize into a stable,hydrous crystallitic solid, without further or substantial additions ofheat and within a period of time shortly after it has been prepared.

The temperature at which the solutions are prepared is, for the mostpart, within the range of approximately 100 C. to-140" C. at atmosphericpressure. If the temperature is lower, then subsequent additions of heatmay be necessary to crystallize th liquid. As disclosed in my copendingapplication, the life of these liquids during which they may becrystallized is relatively short. If the materials are not crystallizedduring this useful period of life, they tend to deteriorate into mushymasses. Therefore, the lower limit of the temperature need be such thatcrystallization proceeds when the liquor is permitted to stand for ashort period of time directly after its preparation. On the other hand,if the temperature be too high, or if the high temperature be maintainedfor a prolonged peroid, then there is dangerof actual dehydration of thecrystals after they have formed. This is undesirable because thedehydrated or anhydrous substances are much more diflicult to dissolvethan those which are hydrated.

The feature of the present invention which makes it particularly usefulin the commercial production of the alkaline silicates of the generalortho range is that the liquors may be prepared in appropriate tanks orvessels at the elevated temperature and then be permitted to crystallizeto solid cakes without further processing.

The solid cakes exhibit a lamellar crystal structure and, for thisreason, these cakes are frangible and therefore specifically suited tobe ground in the conventional grinding mills which I are available inmost of the silicate plants.

Further drying before grinding is unnecessary. Granular materialscomposed of particles of specific and predetermined size are produceddirectly from the cakes by the employment of conventional sieves.

There is at times slight exudation of liquid at the interfaces betweenthe crystal plates of the lamellar structure. This exudate is small inquantity and, when it appears, is visible only as a thin film of liquidupon crushed fragments. These fragments and the cakes in which they arecontained are crushed and comminuted in the usual way, and the'exudatedoes not cause complications in the grinding or crushing or sievingprocedure. Sometimes this exudate is expelled from the mass of a cake asthe crystallization-of it proceeds to completion, and collects as aliquid layer at the top of the cake. When this occurs this liquid issimply. drained off by pouring it from the crystallizing pan shortlyafter the material has solidified, and the crushing is next done in theusual manner. 7

The products which are so produced are stable; they do not become cakedor deteriorate when they are stored in the containers for extendedstorage periods, and they are further very valuable for the reason thatthe water of hydration which they contain makes them dissolve veryeasily and quickly in water.

Grinding is best done while the cakes or I crushed material are stillhot. The silicate liquor preferably is established in a drum, or pan orkettle equipped either with a steam heating coil or with appropriateburners. The kettle or pan also should be equipped with a removablemechanical mixer capable of effecting dissolution of the sodium oxide,water and silicon dioxide components with one another during thepreparation of the liquor. The liquor prepared in the kettle nextdischarged is permittedto stand as is, until it solidifies tocrystallitic solid state, after which it is removed therefrom. Thekettles preferably are of conical shape, so that the cakes drop out fromthem easily, when they are overturned. Expansion of the material takesplace during the crystallization and the kettles are best "constructedto accommodate an expansion of onequarter to one-half inch incircumference for each 3 feet of circumference, without buckling.

In place of casting the liquor directly in the pans from a preparingkettle, small quantities of the material may be made directly in thecasting pans or other suitable containers and permitted therein tocrystallize. I

The following examples will illustrate the commercial practice of theinvention with the employment of several different sources of silicondioxide. I

EXAMPLE 1 Preparation of the composition 1.75Na z0--1Sioz-'5.Hz0

from sodium metasilicate EXAMPLE 2 Preparation of hydrated sodiumorthosilicate Na4Sio4-6HzO, from sodium metasilicate To sodiummetasilicate liquor (Na2S ios-5H2O) at its boiling temperature,approximately 116- 118 C., caustic soda (76% lye flake) is added in thefollowing proportions:

Parts by weight Metasilicate liquor 200 Caustic soda (76% lye flake)76.9

Thesizev of the batch preferably should be such that not much longerthan 15-30 seconds of time is required for the actual addition of thecaustic. The dissolution, of course, is carried out with rapid stirring.The stirring is continued for about 45 seconds longer, at which point oftime the solution begins visibly to thicken. It will be found that thecaustic soda has completely dissolved within this interval of time.After aging approximately one-half hour the mass of material will haveset to a hard, frangible, thermally crystallized body of hydrated sodiumorthosilicate. Thecontainer may be insulated to hold the sensible heat,if desired. While still hot, if desirous, the cake of sodiumorthosilicate may be crushed and ground to any desired degree offineness; in such case, the sensible heat in the material willbe foundsuificient to remove any surface moisture that may be present.

, EJQAMPLE 3 Preparation 09 the composition,

The water is mixed with thesoc'lium metasilicate liquor and theresulting solution heated to the boiling point. The caustic soda is thendissolved in the sodium metasilicate solution in the manner described inExample 2 to produce thermal crystallization.

EXAMPLE 4 Preparation of sodium orthosilicate,

N a4S2'o4 6H2O, from 60 Baum silicate of soda (waterglass) Silicate ofsoda of 60 Baum, which is the preferred starting point according to thisexample, has a molecular ratio of lNazO to about 1.938102. The followinganalysis is typical of this grade:

Per cent NazO 18.7 Sioz 35.0 H2O 46.3

Total"; l 100.0

According to this method of preparation of orthosilicate, approximately141.1 parts by weight of caustic soda (76% lye flake), the preferredsource of NazO, is dissolved with rapid stirring in 200 parts by weightof the 60 Baum silicate of soda at a temperature of 80 to 90 C'.' Thedissolution of the caustic soda is accompanied by a rise in temperatureof the solution of approximately 30 to 40 C. After solution of thecaustic soda, which occurs in about one minute with rapid stirring, themass of liquid sets to a hard, frangible cake of solid sodiumorthosilicate within approximately one-half hour.

Having described my invention, I claim:

1. A method of preparing a stable, crystalline, hydrous, sodiumsilicate, which method comprises, mixing reagents, at least one of whichis hot and thereby preparing a hot liquor containing approximately 1.75to 2.25 molecular parts of sodium oxide to each molecular part ofsilicon dioxide, and containing an amount of water controlled to provideapproximately 5 to 7 molecules water of hydration and permit ofcrystallization of substantially all of the liquor, without evaporationof water therefrom, the temperature of the prepared hot liquor beingabove 100 C. and capable of effecting thermal crystallization of theliquor, without further addition of heat, when it is permitted to standafter it has been prepared, but not sufiiciently high to evaporate anysubstantial quantity of water therefrom, and cansing substantially allof this liquor to crystallize to solid state by permitting it to standwithout substantial reduction of the elevated temperature untilcrystallization is complete.

2. A method of preparing a stable, crystalline, hydrous, sodiumsilicate, which method comprises, mixing reagents, at least one of whichis hot, and thereby preparing a hot liquor comprised of approximately1.75 to 2.25 molecular parts of sodium oxide. to each molecular part*aeeaae s of silicon dioxide, and an amountoi water suifi- "cient toproduce a hydrateand insufiicient in amount to prevent crystallizationof substantially all of the liquor by "adding caustic soda to hot metasilicate liquor, the preparation of the liquor taking place at atemperature above "100 C. and'sufficiently high to efiectthermalcrystallizationof the liquor-when it is permitted tojstand for a periodof time without substantial reduction of its temperature, andcrystallizing said liquor at said temperature above 100 C. by casting itin pans and therein permitting itto stand without further addition ofheat.

3. Amethod of preparing a stable, crystalline, iydrous, sodium silicate,which; method eomprises the step of mixing and dissolving caustic sodain hot liquid metasilicate in suificient the temperature of the hot metasilicate liquor being such that as the caustic soda is added to it andthe liquor is prepared its temperature is above approximately 100 C. andsufficiently high to cause the liquor to solidify to a hard grindablemass when permitted to stand and then crystallizing said liquor at saidtemperature above approximately 100 C. by permitting it to stand withoutfurther addition of heat.

4. The method of preparing a stable, hydrous, sodium silicate, whichcomprises mixing reagents, at least one of which is hot, and therebypreparing a hot liquor containing approximately 1.75 to 2.25 molecularparts of sodium oxide for each molecular part of silicon dioxide, andcontaining an amount of water s'ufiicient to produce a hydrate but notinsubstantial excess of an amount which will permit of crystallization ofsubstantially all of the liquor to a solid state. without evaporation ofwater, the preparation of the liquor being conducted at an elevatedtemperature which is above 100 C. and sufficiently high to cause theliquor to crystallize, without evaporation of water from it, to a solidstate, when the liquor is permitted to stand for a period of timedirectly after it has been prepared, and then causing said liquor tocrystallize at elevated temperature by permitting it to stand, andfinally grinding the solid material until it is of granular form. r

5. The method of preparing a stable, hydrous, sodium silicate, whichcomprises mixing reagents, at least one of which is hot, and therebypreparing a hot liquor containing approximately 1.75

to 2.25 molecular parts of sodium oxide for each molecular part ofsilicon dioxide and containing an amount of water sufiicient to provideapproximately 5 to 7 molecules of water of hydration, and insufiicienttoprevent crystallization of substantially all of the liquor withoutsubstantial evaporation of water, at a temperature in the range of about100 C. to 140 C., and then permitting the liquor to crystallizeat thistemperature to a hard grindable cake.

6. Ihe method of preparing a stable, hydrous, sodium silicate, whichmethod comprises admixing molten sodium metasilicate with hot causticsoda at a temperature sufliciently high to provide a temperature ofabout 100 C. to 140 0. when the caustic soda has reacted with themetasilicate in such proportion that approximately 1 1.75 to 225'molecular parts of sodium oxide are present for each one molecular partof silicon dioxide,andin the presence of a quantity of 'moisture whichis suflicient in amount to provide about 5 to 7 molecules of water ofhydra- .tion, but which is insuflicient in amount to pre- -ventcrystallization of substantially all of the liquor without substantialevaporation of water, and then permitting the liquor to crystallize atsaid elevated temperature, shortly after it has been prepared, to astable crystallitic solid,

grindable cake. v

7. The method of making a stable, hydrous sodium silicate, which methodcomprises making,

A at an elevated temperature and over a short period of time, a solutionwhich contains approximately 1.75 to 2.25 molecular parts oi sodiumoxide to each molecular part of silicon dioxide and which contains watercalculated in amount to provide approximately 5 to 7 molecules water ofhydration, by combining caustic soda, and

sodium silicate, at least one of which is hot and,

if necessary, Water, in the proportions requisite to provide suchsolution, the elevated temperature at which the solution is made beingabove approximately 100.. C. and sufficiently high to enable thesolution to solidify in substantially GEORGE R. MCDANIEL.

